The present invention generally relates to compressors, and more particularly to a method and an apparatus for recovering energy from an air compressor.
Fluid compressors are often used to produce compressed air for use in an industrial setting such as, for example, a manufacturing plant. The compressor typically supplies compressed air to an air supply header that routes air around the plant for use by various equipment. The compressor produces air of a constant pressure, which may be lowered if necessary for specific equipment by conventional regulators or reducers. Due to varying equipment usage the demand for compressed air is typically not a constant value. Regardless of demand, however, the air compressor continues to work to produce a constant pressure in the supply header. Adjustments must be made in compressor output to account for changes in demand. This adjustment is particularly important with centrifugal compressors which often operate at high speeds with continuous air flow for peak efficiency.
Certain systems employ multiple compressors to deal with the changing demand in the air supply header. These systems routinely bring extra compressors on line during periods of increased demand, and secure extra compressors during periods of low demand. This type of system only provides gross control of the compressed air supply and can not be used to accurately match compressed air supply with the demand.
As a result, most compressed air systems operate so that during periods of lower demand a significant amount of compressed air is bypassed or blown off into the atmosphere to maintain the air system supply header pressure constant. The compressed air that is blown off to the atmosphere represents a significant amount of unused product and potential energy that cannot be recovered. Accordingly, there exists a need for a system that converts the potential energy of the excess compressed air into usable energy in order to recovery of some benefit from this excess compressed air and achieve cost savings and improved in compressor efficiency.
Energy recovery systems are known. For example, U.S. Pat. No. 5,689,141 to Kikkawa et al. (xe2x80x9cKikkawaxe2x80x9d), incorporated by reference herein, discloses a system of using excess energy from a natural gas turbine to generate electricity for an associated industrial facility. However, Kikkawa merely couples the rotating shaft of the gas turbine to a synchronous motor, and does not teach a system in which the potential energy present in a fluid, such as air, is converted to a useful form of energy.
Similarly, U.S. Pat. No. 4,243,892 to Andersson et al. (xe2x80x9cAnderssonxe2x80x9d), incorporated by reference herein, discloses recovery energy in a pumping system that pumps fluid from a lower level to a higher level. Andersson teaches allowing fluid to flow backwards through the pump in order to operate the pump as a turbine and generate electricity through pump""s synchronous motor. Like Kikkawa, Andersson fails to disclose extracting potential energy from a pressurized fluid. Thus, there remains a need for system that converts potential energy present in a pressurized fluid into a useful form of energy. The present invention addresses this need and provides other benefits as well, as described further below.
A compressed air system is provided. The system includes an air compressor for supplying compressed air to a conduit connected to the discharge of the compressor and configured to receive compressed air for delivery to a compressed air supply header. A power generation system connected to the discharge conduit for converting compressed air into energy is provided. A control valve positioned between the power generation system and the discharge conduit for controlling the air supply to the power generation system may be provided. The control valve is preferably configured to open when the supply of compressed air produced by the air compressor exceeds a demand for compressed air in the compressed air supply header.
The system may further include a bypass valve connected to the discharge conduit for controlling the flow of compressed air to atmosphere. In addition, a check valve may be positioned in the discharge conduit upstream of the bypass valve and downstream of the power generation system to prevent back flow from the supply header to the compressor and power generation system. A microprocessor based controller may be provided to control the position of the control valve. Preferably, the controller operates to open the control valve when pressure in the discharge conduit exceeds a predetermined value.
The power generation system may include an air motor, turbine generator or other suitable devices for converting the compressed air into useful energy. The system may supply provide electric power to supplement an electric motor, or to generate electric power to be supplied to a main power grid. The power generation system may be supplied with heated air that has not been passed through a conventional aftercooler located in the discharge conduit.
According to the present invention, a method for recovering energy from a compressed air system is provided. The method comprises the steps of: compressing air in an air compressor; supplying the compressed air to a conduit for supplying equipment requiring compressed air; measuring the pressure of the compressed air in the conduit; diverting a portion of the compressed air in the conduit to an energy recovery system when the air pressure reaches a first predetermined level; and converting the potential energy of the diverted portion of compressed air to electrical energy.
Preferably, a second portion of the compressed air to atmosphere when air pressure in the conduit reaches a second predetermined level greater than the first predetermined level. The diversion of the second portion of compressed air may be secured when the air pressure in the conduit drops below the second predetermined level. As described further below, the method may include supplying electrical energy to a main electrical grid used to power a prime mover for the compressor or to an oil pump for the compressor. The electrical energy may be produced in a turbine generator.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.